Nonionic surfactants in municipal sewage in Israel

Nonionic surfactants are a significant factor in the municipal sewages profile, which, in turn, affects the efficiency of sewage-treatment processes and determines the possibility of sewage-water reuse. Hard (nonbiodegradable), nonionic surfactants are the most commonly used nonionics in Israel, which probably has no parallel in other western industrial countries. In view of the increased share of nonionic surfactants at the expense of anionic surfactants, a worldwide trend, municipal sewages in Israel were expected to contain increasing amounts of nonionic surfactants, unless the ratio between the biodegradable and nonbiodegradable nonionics used was significantly changed. In vivo determinations of nonionic surfactants in representative municipal sewage systems in Israel, applying a modified SDA-cobalt thiocyanate (CTAS) procedure and calibration curves (prepared under in vitro conditions), established typical concentrations of nonionic surfactants in municipal sewage in the northern part of Isreal to be in the range of 3–4 mg/L. Under the particular local situation, a calibration curve derived from a mixture of nonylphenol ethoxylates (NP_8–14), having a slope of 0.165 absorbance units/mg of nonionic, can be reliably used to determine the content of nonionic surfactant of municipal sewage effluents. A correction factor based on the extent of nonionic recovery should be applied to ensure accuracy. All of the results obtained agree with other relevant studies and worldwide trends. The concentration of nonionic surfactants in municipal sewage in Israel appears to be decreasing. The results of the study, selected aspects involved with the determination procedure under in vivo conditions and issues relevant to the problem of nonionic detergents in municipal sewage, are discussed. The contribution of the study toward the improvement of water quality, thus increasing its potential for reuse in Israel (and elsewhere), is emphasized.